Method and means for controlling electric motors.



No 865,813. PATENTED SEPT. 10, 1907. w. H. POWELL.

METHOD AND MEANS FOR CONTROLLING ELECTRIC-MOTORS.

. APPLICATION FILED Jun: so. 1906.

l/yvgNToR WITNESSES Wzlllam H.Powell TTORNEY STATES PATENT OFFICE. WILLIAM H. POWELL, OF NORWOOD, OHIOQASSIGNOR TO ALLIS-CHAIMERS'COMPANY, A CORPORATION OF NEW JERSEY, AND THE BULLOCK ELECTRIC MANUFACTURING COM- PANY, A CORPORATION OF OHIO.

' amnion am) mans iron oorrrnormmo anaemic lo'ron's.

To all whom it mag concern:

Be it known that I, WILLIAI H. Powztn, a citizen of the United States, residing at Norwood, in the county of Hamilton and State of Ohio, have invented certain new and useful Improvements in Methods of and Means for Controlling Electric Motors, of which the following is a full, clear, and exact specification.

' My invention relates to motor control systems, and particularly to control systems for'r'n'ill andhoisting motors. 1

In rolling mills and in mine hoisting machinery it is necemary that the moving parts be quickly and often reversed. Heretofore, steam engines have generally been used for this work. Certain electrical systems for doing the same work have been proposed by others, but these have all been unsatisfactory. Inmy copending application Serial No. 311,827 filed April 16th, 1906 I have illustrated and described a system in which a great many of the difficulties of these prior electrical systems have been overcome. In that application a system is described in which the working motor is supplied with current bya special generator,

' on whose shaft is a fly wheel, there being a single controlling arm which inversely varies in alternate steps the field strengths of the working motor and the special generator. It is sometimes advantageous, however,

'to have both the generator field and the motor field at maximum strength at the same time, and my present invention enables this result to be accomplished.

In one aspect my invention comprises the method of operating an electric motor at variable speed, which consists in succeaiively'and inversely varying its field strength and the 'electromotive forceimprws'ed on its armature, storing as mechanical energy any excess of supplied energy when the load on the motor is light, and supplying said stored energy as electrical energy when the load on themotor is heavy.

In a more specific aspect, my invention comprises the method of operating an electric motor at a variable speed and load which consists in supplying mechanical energy, converting it toelectrical energy, supplying the electrical energy to the motor, successively and inversely' varying the electromotive force of said electrical energy and the field strength ofsaid motor,'storing any excess of the mechanical energy when the power supplied exceeds the power demanded by the load and supplying said stored energy to the motor as electrical energy .when thepower demanded by the load exceeds the power supplied.

In another aspect my invention comprises the method of reversing an electric motor. which consists in first strengthening-its field, then' diminishing to zero the electro-niotive force impressed on its armature, then amof Letterm n. Application am In. so, root. sum-1.. auras.

rsmteass c 10, 1907.

increasingin the reverse direction the electro-motive force impressed on its armature, and finally weakening its field.

-From another point of view my invention consists of a motor control system comprising a motor, a source of current for supplying the motor armature, a second source of current for supplying the motor field windings, and means for successively and inversely varying the electro-motive force of said first source of current and the field strength of thermotor.

In still another aspect my invention consists of a system of motor control, comprising a motor, and means for first increasing the of its field, then di-u minishing to zero the electro-motive. force impressed on its armature, then increasing in the reverse direction erator, and means for allowing said first motor .to decrease in speed when the load on said second motor increases.

Other features of my invention will appear from the following description and accompanying drawings and will be particularly pointed out in the claims.

The single figure of the drawings shows diagrammatically one embodimnt of my invention.

In this figure A is an electric motor of the threephase induction type, though obviously other forms of motors could be used instead. In the. rotor circuit of this motor is astarting resistance l adjustable by means of a short-circuiting bar 2, and a regulating resistance 3 arranged. to be cut-in and out by a solenoid switch 4, which in turn is responsive to the current strengthiri-the primary circuit of the motor, as through a series transformer 5. Other means for varying the speed of motor A may be used if desired. A generator armature B is driven by the motor A, being preferably,

directly connected thereto, and on the common shaft of the motor A- and generator- B is a heavyfly-wheel C. The generator B supplies current to the armature D of the working motor. The rnotor D may be used to drive any desired machinery.

The field windings b of the generator, and d of the working motor are suppliedfrom any direct current source through a switch 6. These two field coils are controlled by a single controller H, which ,is arranged to vary the resistance in circuit respectively with 55 open condition of this switch during starting. .After these two field coils and to reverse the current .in the coil b. The arm or handle h of this controllr'is divided into several electrically distinct parts. There impossible if thesame resistance is used for both field are two sets of variable resistances, one set of which, resistances 14 and 15, are for the field circuit of the generator, and the other set, 16 and 17, for the.field circuit of the working motor. With separate resistances for the generator and motor-field circuits, it is possible to make the motor and generatorsubstantial duplicates of each other, which, because of the different variations to be produced in the two fields, is generally circuits. For this reason it is deemed best to have separate resistances for the two field circuits, although in some instances a single resistance may suffice. If desired, instead of having the resistances 14 and 15 separate, the contacts of one may be connected to the corresponding contacts of the other, one of these resistances being omitted. The same cross connection may be applied to the contacts of resistances 16 and 17.

The controller is arranged so that when its arm h is moved on one side of the vertical, the resistances '14 and-17 are successively varied to control the speed of the motor D in one direction, and when moved on I the other side of the vertical, the resistances 15 and 16 are successively varied to control the motor D in the other direction, the direction of current through the coil b being reversed as the arm in passes through its verticalposition. Betweenthe segments 7 and- 8 of the controller is arranged a resistance 9 to take up the -field discharge when the circuit through the coil b is broken. The resistance 9 is aided in this by a high esistance 11 permanently connected across the coil b..

A non-inductive resistance 13 is connected in series with the field coil b. This resistance hasan ohmic value several times as great as that of the field 'coil with which it isin series. The purpose of this resistance is to diminish the time constant of the field mag not b, for the time constant -of a circuit is a function of its inductance divided by its resistance. Therefore by increasing the resistance of the field circuit .without increasing its inductance, the current strength being mary circuit of motor A is closed and the motor started,

by moving the bar 2 to cut out the starting resistance -1.

The switch 4 is held open by its solenoid at this time because of the heavy current required for starting the motor. If desired, other means may be used to insure the the motorhas gained sufficient speed and the starting resistance has been'cut out, the solenoid switch is allowed to close to cut out resistance 3 because of-the de crease in the primary current of motor The flywheel 0 and generator armature B are also started with the motor A and the fly-wheel stores mechanical energy by its rotation. During this starting the arm his pref erably in its vertical or off position.- The switch 6 now being closed, the motor field of is at its strongest,

for it has none of the variableresistance 16 or 17in cirmoves, say anti-clockwise, it first connects the field coil b tothe direct current source through the whole resistance 14, and then gradually cuts-said resistance out of circuit with coil b. When the entire resistance 14 has been cut out of circuit, the field coil b is at its strongest and the electromotive force delivered by the armature- -B has reached its maximum. So far no change has been made in the resistance in circuit with field coil d and therefore the field strength of the working motor is also still at its maximum. Thus at this time the motor D has a very strong torque. A further movement of the causing said motor to still further increase in speed. The speed which the motor D acquires depends upon the extent of movement of the arm h, the full speed being reached when the full resistance 17 has been included in circuit with the field coil d.

If the load is heavy the-working motor requires more power for its starting than the motor A can furnish. The current rising in the primary of transformer 5 by reason of this heavy load, the switch 4 is opened, thus inserting resistance 3 into'the rotor circuit of inotofA. This increases the slip of motor A and permits the motor to slow down, thus allowing the fiy-wheel C to givenp some of the mechanical energy it has stored, which energy helps the motor A to drive generator B to supply electrical energy at the rate demanded by the motor D to drive its load. I

As the arm is moved backward toward the vertical the field d is first strengthened and after it has reached its full strength the field b is weakened to decrease the electromotive force of armature B. Both the'increasing of its field strength and the diminishing of the electromotive force impressed on its armature slow down the motor D, causing it to actas a generator-to supply current to the armature B, the latter now serving as a motor to help restore'energy to the fly-wheel C. There is v a powerful braking effect on the working motor due to its acting as'a, generator. The diminished current in the primary of transformer also causes the solenoid switch 4 to close, thereby increasing the speed of motor A so that the latter may also supply energy to the flywheel 0. The fly-wheel thus stores up any excess of.

energy supplied when the rate of such supply exceeds the rate at which energy is demanded by the working motor, and gives up said stored energy whenever the.

rate of energy demanded is greater than the rate of energy supplied. When the arm h leaves the contacts of resistance 14 and slides over the segments 7 and 8, the resistance 9 is connected in circuit with the coil 1b to take the field discharge therefrom, the resistances 11 and 13 assisting in this. When the arm I: is moved in the other direction from the vertical the above cyclelis repeated save that the working motor D is caused to ro tate in the other direction.

With m-yinven'tion it is possible to quickly reverse motors; especially those of large capacity, and to do this the motor A because of the greater uniformity with which energy is demanded of this motor. The capacity ofmachinesBandDmnalsobegreatlyreducedbecause the maximum current and maximum voltage are demanded by the working motor at nearly the same time. Another great advantage of my invention is that the maximum armature current is lem, and flows when the generator has a stronger field magnetism, commutation being thus greatly existed. There are many other advantages of my invention which it is not necemry to point out, as they will be obvious to any one skilled in the'art.

' energy When I use the term inversely in this description and in the claims, I do not wish to limit myself to exact inverse proportion, but intend the term to include any increase in one and decrease in the other of the two things specified. .L

I have described my'invention inwhat I now consider to be its preferred form, but I aim to cover all skilled in the art.

1. The method of operating an electric motor at variable those obvious modifications which readily occur to one speed, which consists in supplyingmechanical energy at,

a substantially uniform rate, transforming the mechanical into electrical energy, supplying the electrical energy to the motor, successively and inversely varying the clectromotive force of the electrical energy and the lield strength of the motor, storing any excess of the supplied mechanical energy beyond that demanded by the motor at any time, and supplying said stored energy to the motor whenever required.

2. The method of operating an electric motor at variable speed, which consists in successively and inversely varying its field strength and the electromo'tive force impressed on its armature storing as mechanical energy any excess of supplied energy when the load on the motor is light, and Supplying said stored energy as electrical energy when the load on the motor is heavy.

ii. The method of operating an electric motor, at variable, speed. which consists in converting mechanical energy into electrical energy, supplying the electrical energy to the motor, successively and inversely varying the electromotlve force of the electrical energy and the field strength of the motor. storing any excess of the mechanical energy when its rate of supply exceeds the power demanded by the .motor at any tlmepand supplying said stored energy to the motor as electrical energy Whenever the power demanded by the motor is above that normally supplied.

4. The method of regulating the speed of an electric motor, which consists in supplying mechanical energy at a substantially uniform rate, converting said mechanical energy into electrical energy at a variable rate, supplying the electrical energy to the-armature of the motor, energizlng the field of the motor from a separate source, -successlvely and inversely varyingthe electromotive force of the electrical energysnd the field strength of the motor, storing any" excess of mechanical energy whenever its rate of supply exceeds the rate at which energy isrequired by the motor load, and supplying said stored energy to the motor as electrical energy whenever energy is demanded by the load at a rate which exceeds the nor-.

mal rate at which the mechanical energy is supplied.

5. The method of reversing an electric motor, which ture, supplying the field of the motor entirely from a sep- 8. The method of operating an electric motor at a vnrl- 'able speed and load, consisting in successively and inversely varying its field strength and the electromotive force impressed on its armature, storing as mechanical energy the excess of energy when the supplied power on ceeds the power demanded by the load, and supplying said stored energy to the motor as electrical energy when the power demanded by the load exceeds the supplied power.

9. The method of operating an electric motor at a variable speed and load, \vhich consists in supplying mechanical energy, converting it into electrical energy, supplying the electrltal energy to the motor, successively and inversely varying the electromotlve force of the electrical energy and the field strength of the motor, storing any excess of the mechanical energy supplied when its rate of supply exceeds the rate at which energy is demanded by v the load, and supplying said stored energy to the motor as electrical energy when the rate at which energy is tiemanded by the load exceeds the rate at which the mechanical energy is supplied. 1

10. A system of motor control, comprising a dynamoeiectric generator driven by a source of substantially constant power, a motor supplied by the generator, means for successively and inversely varying the electromotive force of the generator and the field strength of the motor, and means for mechanically storing any excess of the energy supplied by the driving source and supplying said stored energy to the motor whenever, required.

11. A system of motor control, comprising a motor, means for successively and linversely varying its field strength and the electromotlveforce impressed on its armature, and means for mechanically storing any excess of supplied energy when the motor load is light and for supplying said stored energy to the motor as.eiect.ricnl energy when the motor load is heavy.

12. A system of motor control, comprising a dynamoelectric generator, a motor supplied thereby, means for successively and inversely varying the electro-motive force of the generator and the field strength of the motor, means for storing any excess of the mechanical energy supplied to the generator when its rate of supply exceeds the power demanded by the motor at any time, and means for causing said stored energy tobe supplied to the motor whenever the power demanded by the motor is above that normally supplied. 7 3

18 A motor control system, comprising a source of substantially constant mechanical power, a generator driven thereby, a variably loaded motor whose armature is supplied by thegcnerator, a separate source of current which supplies the field of the motor, means for successively and and the field strength of the motor, means for storing any excess of the mechanical energy supplied by the source when.its rate of supply exceeds the rate at which energy is demanded by the load on the motor, and means for caus lug said stored energy to be supplied to the motor as electrlcal energy when energy demanded by the load'at a rate which exceeds the normal rate at which the mechanical energy is supplied.

14. A system of motor control, comprising a motor, means for first increasing the strength of its; field, then diminishingto nero the electromotive force impressed on its armature, then increasing in the reverse direction the electromotive force impressed on its armature, and finally weakening its' field.

15. A system of motor control comprising an electric motor, a source of current supplying the motor armature, a

second source of current supplying the motor field coil, and

means for first'strengthening the motor field, then diminishing to zero the electromotive force of said first source of current, then increasing in the reverse direction the electl'omotive force of said first source of current, and finally weakening the motor field.

16. A motor control system, comprising a motor, means for successively and inversely varying its field strength -and.the electromotive force impressed on' its armature, means for mechanically storing any excess of energy when the supplied power exceeds the power demanded-by the motor load, and means for causing said stored energy to be supplied to the motor as electrical energy when the power demanded by the motor load exceeds the supplied power.

17. A motor control system, comprising a source of mechanical power, a dynamo-electric generator driven thereby, a motor supplied by the generator, means for successively-and inversely varying the electromotive force of said generator and the field strength of said motor, means for storing any excess of mechanical energy supplied by said source when its rate of supply exceeds the rate at which energy is demanded by the motor load, and means for causing said stored energy to be supplied to the motor as electrical energy when energy is demanded by the motor load at n rate which, exceeds the rate at which mechanical energy is supplied by the source. 18. In combination, a. source of power, .a generator driven thereby, a motor supplied by the generator, means for successively and inversely varying the field strengths of the generator and the motor, a fiy-wheel on the'shaft of the power source, and means for causingthe fiy-wheel to give up its energy when the load on the motor rises above the normal. I I

19. In' combination, a source' of power, a generator driven thereby, a motor supplied by the generator, means for successively and inversely varying the resistances of the field circuits of the generator and the motor, a fiywheel on the generator shaft, and means for allowing said fiy-wheel to give up its energy when the motor load rises above normal.

20. A system of motor control, comprising a motor, a

generator supplying said motora fiy-wheel on said generator shaft, and means for successively and inversely varying the field strengths of said' generator and said motor.

21. A system of motor;control, comprising a motor, a generator supplying said motor, a fly-wheel.on said generator shaft, means for successively and inversely varying the field strengths of said generator and said motor, and means for permitting the fiy-wheel to give up its energy when the load on the motor is heavy.

.22. A system of motor control, comprising a motor, a

- -generator supplying said motor, a fly-wheel on said gengenerator "supplying said motor, a Lily-wheel on said generator sha'ft meAns for successivelyand inversely varying the field strengths-of said generator and said motor, and means for causing the generator to run slower. when the motor load isiheavy than when the motor load is light.

24. A system'of motor control, comprising a motor, a generator supplying the armature of said motor, a separate source of current supplying the. fields of said generator and said motor, a iiy-wheel'on said generator shaft,

and means for successively and inversely varying the field strengths of said generator and said motor.

25L'A system of motor control, comprising a motor, a generator supplying the armatureof said motor, a fly-wheel onmssid generator shaft, means for successively and inversely varying the field strengths of said generator and saldmotor, and means for allowing the fly-wheel to give up its energy when the load on the motor is heavy.

26. A system of motor control, comprising a motor, a generator supplying the armature thereof, a fiy-wheel on 27. A system of motor control, comprising a motor, a

generator supplying the armature of said motor, a fly-wheel on 'said generator shaft, means for successively and inversely varying the field strengths of said generator and said motor, and means for permitting the generator to run slower when the motor is heavily loaded than when the motor is lightly loaded.

28. A system of motor control, comprising an induction motor, a generator driven thereby, a fiy-wheel on the shaft of said induction motor, a -worl ing motor supplied by said' generator, and means for successively and inversely varying the field strengths of the working motor and the electromotive force of the generator. I I 29. A system 'of motor control, comprising an induction motor, a generator directly connected thereto, a fiy-wheel on the shaft of the induction motor, a working motor supplied by the generator, and means for successively and inversely varying the field strengths of the generator; and the working motor. V I

30. A system of motor control, comprising an induction motor, a generator driven thereby, a fly-wheel on the shaft of the generator, a working motor supplied by the generator, means for successively and inversely varying the field strength of the working motor and the electromotive force of the generator, and means for decreasing the speed of the induction motor when a heavy load ispiaced on the separate source of current for supplying the field coils of the generator and the motor, a permanent resistance in the generator field circuit, variable'resistances in the field circuits of the generator and the motor, and-means for successively and inversely varying said variable resistances.

32. A system of motor control, comprising a generator, 9. motor wh'ose armature is supplied thereby, a separate source of current for supplying the field magnets of the generator and the motor, and means for successively and inversely varying the resistances of said field circuits and for reversing the direction of current through the generator field circuit. I 33. A system of motor control, comprising a generator, 11 motor whose armature is supplied thereby, a separate source of current supplying the field magnets of the gen- 'erator and the motor, means for successively'and inversely varying the resistances of said. field circuits and for reversing the direction-of current through the generator field circuit, and a permanent resistance in the generator field circuit. I f

34. A system of motor control, comprising a generator, '11 motor, and means for successively and inversely varying the field strengths of the generator and the motor, and for reversing the direction of current in the generator field circuit. a

35. A system of motor control, comprising a generator, a motor whose'armature is supplied thereby, a separate source of current supplying the field coils of the generator and 'themotor, and means for successivelyand inversely varying theresis'tances' of said field circuits and for reversing the current in said generator field circuit after its resistance has been in'c reasedto the maximum.

36. A system of'.motor control, comprising a source 0! a second motor supplied by said generator,.means for successaid first motor to decrease in speedwhen-the load on the second motor increases. I I

37. Asystem of motor control, comprising a generator,

,a motor supplied thereby, means for successively and in 'verseiyvarying the field strengths of said generator and said motor and reversing said generator field, and a re-- the generator shaft, means for permitting thefiy-wheel to sistance permanently in said generator field circuit.

38. A system of motor control, comprising a generator, a motor supplied thereby, means for successively and in-. versely varying the tield strengths of said generator and said motor and for reversing said generator field, and re-' sistances permanently in the field circuits of the generator and themotor.

31). A system of motor control, comprising a generator, :1 motor supplied thereby, resistances in the field circuits of said generator and said motor, means for successively and inversely varying said resistances, and for reversing the current in the generator field circuit after the full resistance in said circuit has been cut in, and a high resistance connected across the generator field terminals.

40. A system of motor control, comprising a generator, a motor supplied thereby, variable resistances arranged to be connected in the field circuits of the generator and motor respectively, and a regulating and reversing rheostat so connected and arranged that it successively and inverseiy varies the resistances of the generator and motor field circuits, and can reverse the current in the generator field circuit after the resistance in said circuit has reached its maximum. p

41. A system of motor coutrol, comprising a generator, a motor whose armature is supplied thereby, a separate source of current for supplying the field circuits of said motor and said generator, and a regulating and reversing rheostat so connected and arranged that it can successively and inversely vary the resistances 0! said field circuits. and reverse the current in the generator field circuit when the motor field circuit has its minimum resistance.

4;. A system of motor control. comprising a generator, a motor supplied thereby. separate variable resistances for tho field circuits of the generator and the motor, and a single controller arranged to increase the motor speed by first cutting all of one of the resistances out of the generator iield circuit, and then cutting all of the other resistanee into 'the motor-field circuit.

43. A system of motor control, comprising a generator, a motor supplied thereby, separate variable resistances for the field circuits of the generator and the motor, and a single controller arranged to vary said resistances successively and inversely. Q r

from its source of supply.

44. A system of motor control, comprising a generator,

:1 motor su plied thereby, separate variable resistances or I the fleld circuits 0! said generator and motor, and a single controller arranged to vary either 0! said resistances when the other resistance is tully cut out.

45. A system of motor control, comprising a generator, a motor supplied thereby, separate variable resistances for the hold circuits of the generator and the motor, and a single controller arranged to vary the motor speed by first gradually cutting out all of one resistance from its circuit and then gradually cutting all of the other resistance into its circuit.

46. A system of motor control, comprising a generator,

versing the cuilent in the generator field circuit after the full resistance. in said circuit has been cut in, and a resistance arranged to be connected across the terminals of the generator field circuit when said circuit is disconnected 48. A system of motor control, comprising a generator,

a motor supplied thereby, and a single controller so connected and arranged that as its arm is moved from ofif position, the generator field circuit is first closed, and the resistance of said .circuit gradually decreased to a minimum and then the resistance or the motor field circuit gradually increased to a maximum.

49. A motor control system, comprising a purely separately excited motor, a generator supplying the armature of said motor, and means for successively and inversely varying the field strengths of said generator and said motor.

in testimony whereof 1 Mil: my signature, in the presence of two witnesses.

WiLLiAM .n. POWELL.

Witnesses Geo. B. Scum-1r, Fnno J Krusnr. 

